A D2D communication network means a network in which neighbor devices (or Mobile Stations (MSs)) perform communication directly without an infrastructure composed of centralized Access Points (APs) such as Base Stations (BSs) or APs. In the D2D communication network, an MS performs a discovery process of recognizing that there are MSs which are geographically close to each other to establish a radio link with a specific neighbor MS and transmit data with the linked MS. In this discovery process, MSs can be classified into a discovery MS (or discovery device) which recognizes that there are peripheral MSs and discovered MSs which allow peripheral MSs to recognize their existence. Herein, one MS can operate as a discovered MS while operating as a discovery MS.
A discovery method in the well-known D2D communication network can be classified into a distributed method and a centralized method. First of all, in the distributed method, a discovered MS transmits a discovery signal or a discovery message per certain period and a discovery MS receives the discovery signal or the discovery message and recognizes the discovered MS which transmits the discovery signal or the discovery message as a neighbor MS. That is, in the distributed method, several discovered MSs transmit their discovery signals alternately and a discovery MS receives the discovery signal such that the discovery MS recognize the existence of the discovered MS. Herein, because the discovered MS may not know the existence of the discovery MS, it must transmit the discovery message using its resources acquired from all discovery resources. Because the discovery MS may not know the existence of the discovered MS, it must search all discovery resources to receive the discovery signal. That is, although there is no discovery MS within a neighbor region, because the discovered MS does not recognize it, it transmits a discovery signal. Although there is no discovered MS within a neighbor region, because the discovery MS does not recognize it, it attempts to receive a discovery signal to consume unnecessary power.
Also, in the centralized method, a central node recognizes the existence of discovery MSs and discovered MSs and allocates transmission and reception resources for transmitting discovery signals dynamically. That is, in the centralized method, each MS transmits and receives a discovery signal using resources allocated from the central node and verifies whether there are neighbor MSs. As described above, in the centralized method, dynamical signaling for allocating transmission and reception resources to discovery MSs and discovered MSs must be performed. Herein, because discovery resources must be assigned to a plurality of unspecific discover MSs or a plurality of unspecific discovered MSs, it is necessary to allocate resources to MSs which are far more than the number of MS activated in a general cellular system.